In an automobile, for instance, a speed sensor is installed between a driven gear of a transmission and a speedometer cable to transmit a car speed signal to a transmission control computer. In some devices, the speed signal has been utilized to initiate the operation of an automatic door lock.
The rotary shaft of the speed sensor is typically divided into a first rotary shaft and a second rotary shaft. The former is equipped with a flat coupling protrusion extending from the coupling end thereof, and the latter is provided with a coupling recess in the form of a slit in the end thereof. The aforesaid arrangement permits transmitting the rotary power of the first rotary shaft to the second rotary shaft as a result of fitting the coupling protrusion into the coupling recess. Further, the second rotary shaft is equipped with a permanent magnet for detecting the rotation that results from the first rotary shaft's being coupled to the driven gear. Moreover, the first rotary shaft is allowed to rotate in an eccentric state relative to the second rotary shaft.
When the speed sensor is being fitted to the transmission, the first rotary shaft is first coupled to the driven gear and, simultaneously the coupling protrusion of the first rotary shaft is fitted into the coupling recess of the second rotary shaft.
In order to couple the shafts in the aforesaid conventional arrangement, however, the rotational position of the coupling protrusion must be adjusted to register with the coupling recess, because the driven gear, i.e., the first shaft, is fixed and not rotatable. A disadvantage of such a conventional arrangement is that such coupling requires time and effort.